The present invention relates to the processing of harvested crop material, such as threshing and separation in a combine harvester. More particularly, it relates to rotary separators of the helical or spiral flow path-type, commonly called axial flow, in which threshed grain is separated from material other than grain (mog). The invention may also have application in association with axial flow rotary threshing or cleaning mechanisms.
Combines with axial flow rotary separators are well known. Typically, harvested crop material is fed into the annular space between a fixed generally cylindrical and at least partially foraminous separator housing and a rotor rotating concentrically within the housing. Material control elements, such as fixed helically disposed guide vanes on the housing and/or angled blades and bars on the generally cylindrical surface of a rotor, engage the crop material and propel it in a generally helical or spiral path as the rotor rotates. Threshed and separated grain passes outward through the foramina of the housing to a cleaning shoe while the bulk of the material (mostly straw in grain harvesting, for example) is ultimately discharged from a downstream outlet of the housing. Combines with separators of this general type are disclosed in U.S. Pat. Nos. 3,848,609 and 3,982,548. All such known commercial axial flow rotary separators employ rotors with fixed or passive material control elements. The crop engaging elements are typically carried by and fixed rigidly to a rotor core or frame. Rotors of this general type have been developed to perform with acceptable efficiency and consistency in some but not all crop harvesting conditions.
Most known axial flow rotary separators are, at least potentially, volumetrically efficient compared with such devices as the traditional straw walker separator in that a given output is possible from a separator of smaller overall size. However, some characteristics basic to the operation of known axial flow rotary separators, especially those now in commercial use, result in undesirably high levels of specific power consumption and chaff generation (breaking up of straw, etc.).
The force needed to convey material is obtained by friction and compression of the straw mat at the rotor/straw interface. Function depends on relatively small clearances between rotor and housing making the separator relatively sensitive to crop material condition, such as moisture content and straw length. Frictional forces arise from slippage between the rotor and the straw mat and from the movement of the straw mat over the inner surface of the housing, including the particular friction from elements such as helical guide vanes effecting the axial indexing of the straw mat. This requires significantly more energy than separators with mechanisms that provide positive material conveyance, such as straw walkers. Further, because the straw mat is compressed by the rotor and by centrifugal force, penetration of grain through the mat is impeded and must be overcome by the addition of still more energy for agitation of the mat. Thus, a high proportion of the total power consumed by the separator is dissipated in and through the straw mat, frequently resulting in undesirable changes in the structure of the material and including excessive chaff generation requiring relatively more cleaning shoe capacity.